The idea of wireless phone charging is enticing: Set your device down for a quick battery top-up while you eat lunch or wait for a plane. No need to carry tangled cords or hunt for a power outlet. Many phones now offer the feature, and charging docks are starting to pop up in airports and restaurants.
But calling the current technology “wireless” is still a bit of a stretch. True, your phone is no longer tethered to a cable. But the charging dock is plugged into an outlet, and the phone needs to be positioned on the dock in a very specific way. Ultimately, it is not much different from using a power cable.
That looks set to change with two nascent forms of the technology—one of which is truly wireless, allowing a phone to soak up juice by itself from a faraway source. Another big boost could come from Apple, which is likely to introduce wireless charging in upcoming iPhone models, according to news reports. This could bring the concept into the mainstream, and which technology Apple chooses—the current system or a newer version—could influence the industry’s direction.
Today’s cordless charging systems rely on inductive coupling—the same decades-old technology used to charge electric toothbrushes and robot vacuums. A wire coil in the charging dock creates a magnetic field, which flows through a wire coil inside the phone, creating an alternating current that charges the battery. Because the transmitting and receiving coils have to face each other just millimeters apart, the phone needs to be placed in a specific position on the dock. The process is also not very energy efficient, and relatively slow—fully charging a Samsung Galaxy S7 takes over three hours.
One advanced technology looks set to be faster, and able to free users from charging docks. Called resonant coupling, it is an upscale cousin of inductive coupling, involving the same basic setup but with a few extra coils and electronic circuits in both the charger and phone. The extra elements make the transmission coil more efficient and tune it to a magnetic field at a particular frequency, says Alex Gruzen, CEO of WiTricity, a Massachusetts Institute of Technology spinoff that is commercializing resonance charging. “Then something magical happens,” Gruzen explains. “Suddenly the source coil and receiver coil don’t have to be perfectly aligned anymore, and don’t have to be the same size.”
The charging mat can now be over a foot away, can move power just as quickly as a hard wire and can transfer that energy through solid surfaces. That means a charger can be mounted under a table, making it a large charging surface for multiple devices—so users can plop down their phones anywhere on it. “You could ‘power snack’ through the day, charging a bit at a time,” Gruzen says.
The Galaxy S6 and a few other phones now offer resonant charging. But the technology’s high power-transfer rate makes it useful for more than just phones. At the Consumer Electronics show in Las Vegas in January, Dell unveiled a Latitude tablet containing Witricity’s resonance-charging receiver. Gruzen says they are now working with General Motors to develop a charging mat that sits on a garage floor. A driver would simply pull up an electric car for an automatic recharge. This technology might be available in vehicles as soon as 2018, Gruzen says. Wireless charging will also make things easier for autonomous vehicles, he adds: “You can’t have a fleet of driverless Uber cars if they all need to be plugged in.”
Resonance coupling still does not offer quite enough enough for some. Start-ups Energous and Ossia are working on a different charging technology that could power devices from across a room or even a house. It does this by sending power over radio-frequency waves, much like wi-fi base stations broadcast internet signals. These companies have been promising to deliver long-range chargers for over a year now. Energous CEO Steve Rizzone recently told The Verge that the company’s wireless transmitters, which can charge devices from several feet away, will be shipped later in 2017.
Longer charging distances, however, might come with a trade-off. One challenge posed by long-range charging is that “the efficiency is too low, costs are high and the electromagnetic emissions are so high that these products might have difficulty passing regulatory approval,” says Menno Treffers, chairman of the Wireless Power Consortium (WPC), a global manufacturers’ organization that oversees standards for inductive and resonance charging. He believes this technology might be better suited to powering smaller devices like hearing aids, activity trackers, thermostats and smoke detectors, which need less than one watt of power.
That is not to say it could not be used for phones. In fact, all three technologies could have a place in the wireless-charging future, says David Green, research manager for wireless power at U.K.-based market analysis firm IHS Markit. High-power inductive and resonance charging could quickly recharge phones over short distances whereas the trickle of power from long-range radio-frequency transfer could keep the batteries topped up.
Many in the industry are now watching Apple to see which technology it chooses for its iPhone. The company already offers inductive charging on its smartwatch, so it could go with the same method for its phones. On the other hand, its recent move to join the WPC could mean iPhones will come with inductive or resonance charging. And given Energous’s recent deal with Apple chip supplier Dialog Semiconductor, Apple might also be working on long-range wireless power transfer for phones, according to VentureBeat. Meanwhile J. P. Morgan analyst Harlan Sur speculates that Apple might come out with a customized wireless-charging platform built by Broadcom.
Whichever technology Apple picks, its decision could yank wireless charging into the mainstream. No one can predict what Apple CEO Tim Cook plans, Gruzen says, but “all signals are that something’s cooking.”